Solenoids are well-known and are used to perform a wide range of functions including latching, braking, switching, clamping, connecting, etc. In the automotive industry specifically solenoids are used to actuate various mechanisms including locking mechanism, valves, etc.
When current is supplied to a solenoid, the solenoid transduces the flow to a magnetic force that can cause mechanical displacement of a movable part of the solenoid, i.e. the armature/plunger. Generally, in order to maintain the displacement of the armature, the solenoid has to be continuously energized. It has been previously discovered that by selecting the correct materials from which to manufacture the parts of the solenoid, one can take advantage of residual magnetism in the solenoid parts after energization of the solenoid to hold the armature in an engaged position without having to continuously energize the solenoid. In other words, when the coil of the solenoid is de-energized, the residual magnetism in the solenoid parts alone is sufficient to maintain the armature in an engaged position.
It is often desirable or necessary to determine the position of a mechanism that is operated by a solenoid or the location of a solenoid armature itself. The prior art includes many systems to determine the position of a solenoid. Typically these systems use some form of position feedback using a variety of sensors that verify the mechanism has achieved the desired mechanical state after the solenoid has been energized. These systems can include multiple sensors, wiring for the sensors and connectors adding significant cost and additional failure modes that need to be avoided.
In addition, other previous attempts to sense the position of an armature have required an interruption in power to vary the current levels to enable the system to monitor a change in current and correlate that change to a change in position of the armature. In these systems the solenoid materials are already highly saturated magnetically by the energized solenoid and, therefore, the variation in current rise times at these high current levels is not large and difficult to detect.
In view of the disadvantages associated with the prior art systems, it would be advantageous for a system to avoid additional sensors, wiring and connectors to lower the cost of the system and remove possible system failure modes.